Field of the Invention
The present invention relates to a gate driver and to a display device including the gate driver.
Discussion of the Related Art
With advancement of information society, requirements for display devices displaying an image have increased more and more in various forms. Accordingly, various flat panel display (FPD) devices have been developed and brought into the market which can reduce weight and volume which are demerits of cathode ray tubes. Various flat panel display devices such as a liquid crystal display (LCD), a plasma display panel (PDP), an organic light emitting diode (OLED) have been utilized.
Such a flat panel display device includes a display panel including data lines, gate lines, and pixels connected to the data lines and the gate lines, a gate driver supplying gate signals to the gate lines, and a data driver supplying data voltages to the data lines. The gate driver can be formed in a non-display area of the display panel and includes stages including plural transistors to supply the gate lines with gate signals which swing between a gate-high voltage and a gate-low voltage.
Each stage includes a pull-up node, a pull-down node, a pull-up transistor outputting a gate-high voltage when the pull-up node is charged, a pull-down transistor outputting a gate-low voltage when the pull-down node is charged, and a node controller controlling charging and discharging of the pull-up node and the pull-down node. At this time, the node controller discharges the pull-down node when the pull-up node is charged so as to stably output the gate-high voltage, and discharges the pull-up node when the pull-down node is charged so as to stably output the gate-low voltage.
FIG. 1 is a graph illustrating a drain-source current corresponding to a gate-source voltage of an N-type MOSFET. Referring to FIG. 1, a threshold voltage of the N-type MOSFET can be negatively shifted due to manufacturing errors, a stress based on long-term driving, or the like. When the threshold voltage Vth of the N-type MOSFET is negatively shifted, a curve representing the drain-source current Ids corresponding to the gate-source voltage Vgs of the N-type MOSFET can be moved to a curve B to which an original curve A is negatively shifted. Accordingly, the transistor of which the threshold voltage is negatively shifted may cause a problem with a leakage current.
On the other hand, a control circuit may include a transistor for removing noise of a pull-up node (hereinafter, referred to as a “noise removing transistor”). When the threshold voltage of the noise removing transistor is negatively shifted as illustrated in FIG. 1, ripples or noise may be reflected in the pull-up node due to the leakage current of the noise removing transistor. Accordingly, the discharge potential of the pull-up node is fluctuated and thus there may be a problem that a stage abnormally outputs a gate-high voltage.